1. Field of the Invention
The present invention relates to a system for measuring the absorption of light in selected regions of the light spectrum by a diffuse reflector, and more specifically, to a reflectometer utilizing a holographic grating and a photodetector array.
2. Description of the Related Art
There exists a nonlinear but deterministic relationship between the negative log of diffused reflectance (Reflectance density, D.sub.R) at specific wavelengths from a sample containing an absorbing analyte and the concentration, C of the analyte in the sample as shown below: EQU D.sub.R =-log R
and EQU D.sub.R =f(C)
A typical D.sub.R vs. concentration curve is shown in FIG. 1.
By measuring the diffused reflected energy from a given sample at a specific wavelength one can, therefore, estimate the concentration of the absorbing analyte present in the same if an a-priori knowledge of the function f(C) exists at the given wavelength. The D.sub.R vs. C curves are usually established with standard solutions of known concentrations of the analyte.
The wavelength band is analyte-specific and is selected on the basis of constituent molecules of the analyte solutions. The wavelength bands are often experimentally determined from the absorption spectrum and picked up at the highest change of slope.